Archaeologists announced the discovery of a massive 9th-century B.C. stone dam in the City of David, a short distance from the Pool of Siloam in Jerusalem, calling it one of the most significant First Temple–period remains yet revealed in the city.
The structure, uncovered during excavations inside the Jerusalem Walls National Park, measures about 69 feet long, 39 feet high and 26 feet wide, and is described by researchers as the largest dam ever found in Israel and the oldest in Jerusalem. The work was carried out jointly by the Israel Antiquities Authority and the Weizmann Institute of Science and published in the journal Proceedings of the National Academy of Sciences on Aug. 25.
Researchers dated the dam to a narrow window between 805 and 795 B.C., based on radiocarbon analysis of twigs and branches embedded in the mortar; the team said the margin of error for the dating was about 10 years. The construction date places the dam in the Iron Age II period and could coincide with the reign of either King Joash or King Amaziah, the researchers said.
Excavation directors said the dam was designed to collect waters from the Gihon Spring as well as floodwaters flowing down the main valley of ancient Jerusalem, and they framed the work as a deliberate response to climatic conditions. "All the [studied] data pointed to a period of low rainfall in the Land of Israel, interspersed with short and intense storms that could cause flooding," the directors said in a statement, adding that large-scale water systems of the sort represented by the dam would have been a direct response to those conditions.
Eli Escusido, director of the Israel Antiquities Authority, called the find "one of the most impressive and significant First Temple-period remains in Jerusalem," saying it sheds new light on the city’s infrastructure and the range of historical layers present beneath modern Jerusalem.
The discovery sits close to the Pool of Siloam, a site associated in the Christian Gospels with the healing of a man born blind after he washed in the pool at Jesus’ instruction (John 9:10–11). The pool itself was rediscovered in 2004 and has since been the focus of archaeological and tourist attention.
The authors of the PNAS paper and excavation teams noted that the dam’s scale and preservation expand current understanding of water-management practices in Iron Age Jerusalem and contribute to a growing body of recent discoveries across the city. Earlier finds this year referenced by researchers include evidence of an ancient garden at the Church of the Holy Sepulchre and a coin minted shortly before the destruction of the Second Temple, underscoring continued archaeological activity in Jerusalem.
The research team said analysis of the construction method and materials, combined with the precise radiocarbon dating, allows for a clearer reconstruction of how ancient Jerusalem coped with environmental stressors while developing complex urban infrastructure. They characterized the dam as both an engineering response to local hydrology and a measure intended to secure water supplies during a period of climatic variability.
Publication of the study and release of the excavation results follow ongoing efforts by Israeli authorities and scientific partners to document and interpret the many overlapping historical periods evident in the City of David.